This invention relates to a frequency synthesizer and more particularly to a frequency synthesizer capable of producing a plurality of signals each having a different frequency.
A type of secure communication system employs a frequency "hopping" technique wherein the signal carrying the intelligence is hopped from one frequency to another in a random manner as far as an unauthorized receiver is concerned to maintain a secure communication system.
To provide signals having different frequencies to be employed with the above type communication system, it is necessary to provide a plurality of signals each having a different frequency and control thereof to randomly transmit these frequencies to an authorized receiver which will detect the various frequencies according to a predetermined program to recover the intelligence carried by the frequency hopping technique. One way of generating or synthesizing the signals having different discrete frequencies is to employ a plurality of oscillators, mixers associated therewith and sideband filters associated with the mixers to enable the selection of the signals having different frequencies. These signals would then be appropriately selected in a random manner to implement the frequency hopped communication system.
One of the problems with the foregoing type synthesizer is stability and phase coherence of the frequency signals produced.